One of two signs in this puzzle
Else clues• 100% sure
• Absolutely certain
• Certain
• Meaning of + on car-battery terminal
• One of your battery's terminals
• Optimistic
• Type of charge
• Upbeat
• Word (suggested by the black shape in this grid's center) that can precede the answers to starred clues
• A film showing a photographic image whose tones correspond to those of the original subject